The present invention relates to a method of reprocessing neutron irradiated corrosion products, irradiation products and other contaminants containing boron carbide (B.sub.4 C) from trim or shut-down elements of nuclear reactors in which the boron carbide, freed from its metal cladding and comminuted, is brought into contact with a hot mixture of sulfuric acid and nitric acid.
To control the neutron flux in breeder reactors, .sup.10 B boron carbide is employed in the control trim and shut-down elements in the appropriate arrangement. For example, the fast breeder reactor SNR 300 in Kalkar, Federal Republic of Germany is equipped with 9 control trim elements and 3 shut-down elements together employing approximately 100 kg .sup.10 B boron carbide. Both of these types of elements are used until the .sup.10 B isotopic enrichment reaches 75% (the initial .sup.10 B isotopic enrichment is about 90%). The discharged absorber rods thus still contain considerable quantities of .sup.10 B. Since .sup.10 B is expensive and its availability is limited, the problem of reprocessing it arises.
If .sup.10 B boron carbide is irradiated with neutrons (conditions in the nuclear reactor) tritium (.sup.3 H) is formed in addition to lithium. The following contaminants of boron carbide are produced: .sup.54 Mn, .sup.55 Fe, .sup.58 Co and .sup.60 Co as well as .sup.14 C. Except for the lithium, all other products are radioactive.